1. Field of the Invention
The present invention relates to engine analyzers and, in particular, to engine analyzers having digital oscilloscope displays.
2. Description of the Prior Art
Digital storage oscilloscopes are well known and typically have two modes of operation, viz., live and freeze. In the live mode, one or more selected input signals are repeatedly sampled by a data acquisition system and the resulting digitized waveform data is displayed on the screen of the oscilloscope and saved in memory. It is known in prior digital engine analyzers to store input waveform data in a memory which is divided up into sections. When the freeze mode is activated, data acquisition is suspended and the most recently-displayed section of waveform data remains "frozen" on the screen. At this point the operator can review previously acquired waveform data that has been saved in memory by recalling it from memory and displaying it on the screen.
It is known to provide digital oscilloscopes with multiple display traces (e.g., two), so that a number of waveforms can be simultaneously displayed. A dual-trace scope can typically be operated in either single-trace mode or dual-trace mode.
It is also known to provide engine analyzers with screen displays which essentially constitute digital oscilloscopes. In the case of a multi-cylinder internal combustion engine, two of the engine waveforms which are commonly displayed on an engine analyzer scope are the primary and secondary ignition voltages which appear, respectively, across the primary and secondary windings of the ignition coil. The primary and secondary waveforms are typically acquired from the engine by means of separate primary and secondary pickup leads. The analyzer also typically has a no. 1 cylinder lead to detect the firing of the no. 1 cylinder so that the analyzer can identify the cylinders once the firing order of the engine is known. Other leads may be utilized to acquire other types of waveforms generated by the engine.
The horizontal scale (also called sweep) of an oscilloscope screen represents time. Broadly speaking, in a digital engine analyzer scope there are two types of sweeps: engine sweeps and fixed-time sweeps. Engine sweeps display a waveform for either a single cylinder ignition or for a complete engine cycle (the time between consecutive firings of the same cylinder), and are typically used to display waveforms related to cylinder ignition events. For engine sweeps, the analyzer includes means for identifying the cylinder firings in the stored waveform data. Engine sweeps may be of any of three different types: cylinder, parade and raster. In a cylinder sweep, only a single cylinder waveform is displayed. In parade and raster sweeps, all of the cylinders for a complete engine cycle are displayed simultaneously on the screen, the cylinders being displayed in horizontal progression across the width of the screen in a parade sweep and being stacked vertically one atop the other in a raster sweep. Since engine sweeps begin and end with the firing of a cylinder, the time represented by an engine sweep varies with engine speed. Fixed-time sweeps (e.g., 10 ms, 100 ms, etc.) display a fixed period of time across the width of the screen display, and are typically used to display waveforms other than primary and secondary waveforms.
An oscilloscope screen essentially displays snapshots of discrete portions of the waveform representing an electrical signal. The mechanism which determines the starting point for each snapshot is referred to as triggering. Prior digital analyzer scopes have supported three types of triggering, viz., auto, signal and cylinder triggering. Auto triggering occurs randomly on a periodic basis, the repeat rate being determined by the selected horizontal time scale. Signal triggering occurs when the displayed signal crosses a threshold level with either a rising or a falling slope. The threshold level and the slope can typically be set by the user. Cylinder triggering occurs when a selected cylinder of the engine under test is fired. This latter trigger mode is used to examine signals from the electrical system of the engine while synchronizing with a selected cylinder. Cylinder triggering normally requires that the no. 1 pickup and either a primary or secondary signal pickup be connected to the engine.
It is known in prior digital engine analyzers to operate the analyzer in either ignition scope mode or a standard lab scope mode. The ignition scope mode is normally used for analyzing primary and secondary waveforms. The lab scope mode is typically used for analyzing waveforms other than primary and secondary waveforms, the display of which other waveforms utilizes a fixed-time sweep. Accordingly, such prior analyzers must use either auto or signal triggering when operating in the lab scope mode and, similarly, are typically constrained to use cylinder triggering when operating in the cylinder or ignition scope mode. Thus, prior engine analyzers do not permit cylinder triggering when viewing a waveform with a fixed-time sweep.